Research on the development and self-assembly of dissociated embryonic neural tissues reaggregated in rotary cultures will be continued along two main directions. On one hand, Golgi analyses of aggregates prepared from dissociated embryonic chick and mammalian cortices will be extended to very early embryonic stages to ascertain the development of neuronal phenotypes and their pattern of assembly. On the other hand, critical experiments will be performed to determine why serum immunoglobulins of the IgM class present in the culture medium accumulate selectively among neurons in the interstices of the neuropile of embryonic neural tissues maintained in culture. In addition, the total segregation of glial cells from neurons which takes place within aggregates under certain experimental conditions will be further investigated.